External Data
In the context of IBM mainframe systems and z/OS, "external data" refers to any data that originates from sources outside the immediate processing scope of a particular program or application. This typically includes data read from files, databases, message queues, or other systems, rather than data generated internally or hardcoded within the program itself.
Key Characteristics
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- Diverse Sources: Can originate from various mainframe resources such as sequential files (
QSAM), indexed files (VSAM), relational databases (DB2), hierarchical databases (IMS DB), or message queues (MQ). - Input for Processing: Primarily serves as input to drive the logic and operations of mainframe applications, whether for batch jobs, online transactions (
CICS), or utility programs. - Format Variability: Often exists in different formats, including fixed-length records, variable-length records, delimited files, XML, JSON, or specific database structures, frequently encoded in
EBCDIC. - Requires Validation: Due to its external origin, the data's quality, completeness, and adherence to expected formats are not guaranteed, necessitating robust validation and error handling by the consuming application.
- Persistent or Transient: Can be persistent (e.g., records in a
VSAMfile orDB2table) or transient (e.g., messages consumed from anMQqueue). - Separation of Concerns: Facilitates modular application design by separating business logic from the specific data it processes, enhancing flexibility and reusability.
- Diverse Sources: Can originate from various mainframe resources such as sequential files (
Use Cases
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- Batch Processing: A
COBOLbatch program reading a daily transaction file (e.g., aQSAMdataset) to update master records stored in aDB2table. - Online Transaction Processing (CICS): A
CICStransaction retrieving customer details from anIMS DBorDB2based on user input, or sending data to another system viaMQ. - Data Loading and Migration: Loading data from external flat files into a new
DB2database during a system conversion or for initial data population. - Report Generation: A
JCLjob executing aCOBOLprogram that processes multiple input files and database tables to produce a comprehensive business report. - Inter-System Communication: Receiving data feeds from distributed systems (e.g., UNIX, Windows, cloud) via
FTP,SFTP,MQ, orTCP/IPsockets for processing on z/OS.
- Batch Processing: A
Related Concepts
External data is foundational to nearly all mainframe applications, as programs rarely operate in isolation without external input. It is intrinsically linked with JCL for defining input/output datasets (DD statements), COBOL for file and database I/O operations (SELECT, OPEN, READ, WRITE), and database management systems like DB2 and IMS for persistent storage and retrieval. Effective handling of external data is crucial for the functionality, integration, and overall reliability of z/OS systems within the enterprise computing environment.
- Rigorous Data Validation: Implement comprehensive validation routines upon input to ensure external data conforms to expected formats, data types, and business rules, preventing processing errors and data corruption.
- Robust Error Handling: Develop robust error handling mechanisms for all file I/O and database access operations, gracefully managing situations like invalid records, missing files, or database connection failures.
- Standardized Record Layouts: Define and strictly adhere to standardized record layouts and
COPYBOOKSfor all external data files and database tables, ensuring consistency across applications and systems. - Performance Optimization: For high-volume external data, optimize I/O operations by using appropriate access methods (e.g.,
VSAM KSDSfor keyed access), efficient blocking factors, and minimizing redundant data reads. - Security and Access Control: Utilize
RACFor equivalent security managers to implement stringent access controls for all external datasets and database resources, safeguarding data confidentiality and integrity.